Glacial/Interglacial Record of Planktic Foraminifera From the Upwelling Area off Chile

The southern part of the Peru-Chile Current (PCC) is among the least studied regions of the world ocean compared to other Eastern Boundary Currents (EBC). The PCC stands out as the EBC with the longest N-S extension (over 20° of latitude) and a strong continuous upwelling regime resulting in a very high biological productivity and an intense cycling of carbon making the PCC to an important part of the global carbon cycle. We analyzed three gravity cores from the Chilean continental margin between 24° and 30° S to observe the intensity of upwelling and productivity in the PCC during the LGM and the Holocene deduced from planktic foraminifera assemblages. Core GeoB 3375-1 was recovered during the CHIPAL-Expedition of RV Sonne (SO-102) off the Norte Chico, while cores GeoB 7112-5 off Antofagasta and GeoB 7139-2 off Coquimbo were retrieved during the PUCK-Expedition of RV Sonne (SO-156). The age models for the cores are based on accelerator mass spectrometry (AMS) 14C dates and stable oxygen isotope data correlated with the SPECMAP stack. Examination of the faunal composition showed the dominance of six species, which account on average for more than 90% of the total planktic foraminiferal assemblage. The dominant species are N. pachyderma dex. (~30%), G. bulloides (~27%), N. pachyderma sin. (~25%), N. dutertrei (~2%), G. glutinata (~2%) and G. inflata (~6%). Absolute concentrations of planktic foraminifera show a distinct maximum during the LGM. After lower levels during the early Holocene, the concentration drops to very low middle-late Holocene levels. The total planktic foraminifera assemblage shows a considerable change in the species composition between 14 and 12 kyr BP manifested by the distinct relative decrease of the cold water species N. pachyderma sin. and G. inflata opposed by the increase of the relatively warmer water species N. pachyderma dex. and N. dutertrei. Thus, warmer water species become dominant at 12 kyr BP. During the LGM, the species composition and high proportions of G. bulloides and N. pachyderma sin. as well as the total accumulation rates of planktic foraminifera point to a relatively high productivity in the surface waters which can be attributed to strong, but variable coastal upwelling. After 12 kyr BP, changes in the species composition of planktic foraminifera point to a considerable warming. After 8 kyr BP, the foraminiferal accumulation rates drop significantly, indicating low productivity for most of the middle to late Holocene, which is also reflected in the species composition. Thus, the foraminiferal record suggests that more Subtropical Surface Water has been advected to the study area after 12 kyr BP.